1. Field of the Invention
The present invention relates to an apparatus for inspecting a pipeline which measures an inner shape or a wall thickness of a pipeline to inspect a deformation or a corrosion of a pipeline, and more particularly to an apparatus for inspecting a pipeline with ultrasonic beams which inspects a pipeline by detecting an ultrasonic beam signal reflected from a pipe body.
2. Description of the Prior Art
This kind of prior art apparatus is constructed in such a manner that scraper cups are arranged in the front and in the rear of a pig body travelling inside a pipeline and that a pressure difference is made by these scraper cups to propel the pig body by pressure,
This apparatus is provided with a travelling distance measuring device which measures a travelling distance of the pig body by counting the number of a rotation of a rotating body being in contact with the inner surface of the pipe body. The apparatus is also provided with a dent-deformation measuring device which measures a deformation of the pipe body by measuring an angle of arms relative to the axis of the pipe body. A plurality of the arms are fitted to the center of the rear of the pig body, extending radially in contact with the inner surface of scraper cups in the rear and moving toward the inside of the pig body when the scraper cups in the rear are transformed in connection with the deformation of the pipe body which is encountered by the scraper cups during a travel of the pig body.
In case of measuring a wall thickness of a pipe body to determine a corrosion state of the pipe body, there are arranged a magnet having North pole and South pole in the axial direction of the pipe body and a magnetic sensor for measuring a change of the densities of the magnetic flux, which is caused by the magnet and changed by the wall thickness of the pipe body, in the vicinity of the inner surface of the pipe body.
In case of measuring an inner shape or a wall thickness of a pipe body, the data collected by the above-mentioned travelling distance measuring device and the dent-deformation measuring device or by a magnetic sensor are recorded in a data recorder inside the pig body. After the pig body is propelled to travel a predetermined distance inside the pipe body to measure a shape of the pipe body and the pig body is taken out of the pipe body, an inner shape of the pipe body is formed by reading out and processing the collected data with the use of a computer.
The prior art apparatus for inspecting a pipeline as mentioned above can determine where a deformation of a pipe body or a change of a wall thickness is in the axial direction of the pipe body by combining the output of the distance measuring device with the output of the dent-deformation measuring device or the magnetic sensor. It is impossible, however, to know where they are in the circumferential direction of the pipe body. As a result, the prior art apparatus has disadvantages in that it is impossible to recognize the shape of the pipe body.